Among a study group of 196 patients, researchers at Mount Sinai School of Medicine found that nearly 20% lost at least 5% or more of their body weight and experienced a significant decrease in body mass index (BMI) -- a measurement of height and weight -- after undergoing total joint replacement, or arthroplasty. BMI decreases were greater among knee replacement patients (21.5%) than hip replacement patients (16.9%), researchers reported.

Overall, the mean weight of the group dropped from 175 pounds to 172 pounds after surgery. The authors took into account natural weight gain that typically occurs with aging. Patients who had a BMI higher than 30, which indicates obesity, were most likely to experience the greater weight loss after surgery.

The findings suggest total joint replacement may help with weight loss and weight management for overweight patients with osteoarthritis because replacing damaged bone with prosthetics increases patients’ mobility and reduces the pain and disability that accompanies osteoarthritis.

The Study

The study was performed between 2005 and 2007; nearly two-thirds of the group were female and about one third was male. Eighty-nine patients underwent total hip replacement surgery and 107 patients underwent total knee replacement. The patients’ mean age was 67. Follow-up lasted an average of 612 days. The study did not evaluate patients’ pre- and postoperative physical activity levels.

“Total joint arthroplasties are performed with the intent of relieving a patient’s pain and disability,” says study researcher Michael Bronson, MD, chief of joint replacement surgery at Mount Sinai School of Medicine. “Both total knee patients and total hip patients experienced a statistically significant and clinically significant corrected weight loss following surgery, which indicates a healthier overall lifestyle.”

Total joint replacement is a common treatment for advanced osteoarthritis, the most common form of arthritis in which the cartilage between the bones is chronically breaking down. Osteoarthritis affects an estimated 27 million adults and can significantly limit a person’s mobility and contribute to overall disability.

Obesity is an independent risk factor for osteoarthritis of the knee and hip because the excess weight can place strain on the joints and contribute to cartilage breakdown. The researchers note that patients with degenerative bone disease such as osteoarthritis also have a high incidence of obesity, a condition that has been steadily increasing in the United States. An estimated two-thirds of U.S. adults are considered either clinically overweight or obese, meaning they have BMIs of 25 and higher or 30 and higher, respectively.

Bronson noted that more studies of total knee and total hip replacement postoperative patients are needed to evaluate the long-term impact of the surgery on potential weight loss. It is unclear whether other types of treatments for osteoarthritis, including other types of surgical procedures, would yield similar weight loss effects. Postoperative care should also include nutritional guidance and fitness recommendations and goals to support sustained weight loss, the authors say.